U.S. Pat. Nos. 4,485,297 issued Nov. 27, 1984, 4,542,285 issued Sept. 17, 1985, 4,633,068 issued Dec. 30, 1986 and 4,774,397 issued Sept. 27, 1988, all of which are hereby incorporated by reference, disclose flexible sheet heaters including a pair of longitudinally-extending (typically copper) conductors and a semiconductor pattern extending between and electrically connected to the conductors. The heaters there disclosed provide generally superior performance and substantially even heat distribution. One principal use of such heaters has been as ceiling or floor heaters in building living space, e.g., the heaters have been stapled in place between a pair of floor joists, about 2 or 3 inches below floor level, and insulation batts have been placed in the remaining inter-beam space below the heaters.
There has been a need for a relatively inexpensive, and efficient, system for heating other types of space, such as storage areas and large truck trailers.